The invention relates to a method for pre-selecting a gear in a dual-clutch transmission of a utility vehicle, such that tooth-to-tooth situations readily are resolved.
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as buses and construction equipment and/or passenger cars.
Dual clutch transmissions have become increasingly common for personal cars as well as utility vehicles over the last years. A dual clutch transmission is commonly provided with a normally closed (engaged) and a normally open (disengaged) clutch. A spring mechanism is acting upon the normally closed clutch such that it engages if there is no active force holding the clutch open. For the normally open clutch, the spring mechanism acts upon the normally open clutch, such that it disengages if there is no active force holding the clutch closed. The clutches are normally operated by a pressure medium driven actuator. Pressure is built up in the system by a compressor; however during a standstill of the vehicle it can be that the pressure in the system is too low to control the clutches. The normally closed clutch is connected to a first input shaft and the normally open clutch is connected to a second input shaft.
Both the normally closed and normally open clutches are input clutches. Each input clutch is designated one set of gears. The input clutches connect the input shafts to the provider of mechanical energy (e.g. a combustion engine) in the vehicle. In a dual clutch transmission a gear is referred to as preselected when the input shaft used by the gear is in drive connection to the driven wheels, but the associated clutch is disengaged. An active gear is the gear on which the vehicle currently is driving.
To prepare for an up-coming gear shift, the preselected gear is changed before the actual gear shift. This is to enable power shifting or to shorten the power cut-off time during power cut-off shifts. Power shifting is when a gear is changed in the transmission and the combustion engine keeps traction power to the drive line. Power cut-off shift is when the power transfer is cut off between the traction source and the drive fine during shifting, e.g. normal shifting in a standard manual vehicle transmission.
A change of the preselected gear typically includes a synchronization step to enable the engagement of the tooth clutch for the engaging gear. For the engaging step there is always a certain probability to end up in a tooth-tooth situation for a certain time depending on the relative movement of the engaging parts.
Such a tooth-tooth situation can be solved by slightly engaging the open input clutch to create a relative movement between the two engaging parts of the tooth clutch. The actuation of the input clutch is a relative time consuming operation and also causes a delay of the actual gear shifting.
It is desirable to provide a method for controlling a multi-clutch transmission of a vehicle, which method solves or reduces the above mentioned problem.
By the provision of the method which is adapted for a multi-clutch transmission comprising;
a first input shaft, a second input shaft, a first shaft, and a second shaft,
at least a first and second tooth clutch arranged upon different shafts, chosen among; said first input shaft, said second input shaft, said first shaft and said second shaft wherein each of said first and said second tooth clutch is provided with a first and a second member respectively, wherein said first and said second member are in drive connection with one of said first and said second input shaft respectively, and
a central synchronizer (70) provided with a first and a second active state (d1; d2) for increasing or decreasing a speed of the one of the first and second input shaft (12, 13) which is not transferring torque, depending of which of said first and said second state (d1; d2) said central synchronizer is provided in.
A drive connection is defined as two parts that are in connection with each other, such that a drive force/torque can be transferred between the two parts, either directly or indirectly over one or several intermediate parts. A drive connection does not have to be permanent, but can be achieved through engagement of one or several couplings or clutches between the two parts. The tooth clutches can be directly arranged upon the shafts and gearwheels or via any form of connection part. Further a tooth-clutch comprises at least a first and a second member, which are arranged to be engaged with each other in order to enable a drive connection between two parts in the transmission.
The central synchronizer is arranged to speed up or speed down the one of the input shafts, which is not transferring torque, by using the speed of the input shaft, which is transferring torque. The respective input shaft is synched down or synched up relative to the speed of the other input shaft, depending on which shaft is driven and which active state the central synchronizer is arranged in. There are different arrangements of a central synchroniser in order to achieve the two active states. In one exemplary embodiment of the central synchroniser, the first and the second active state directions of the central synchronizer are directed in a first and a second direction, opposite to each other.
Because the not torque transferring input shaft still can be in drive connection with a member of a tooth clutch to be engaged, the central synchronizer can be used to synchronize and desynchronize the first and the second member of a tooth clutch.
Now, the first and the second tooth clutches can be arranged in an engaged and a disengaged position, whereby in said engaged position the first and the tooth clutches enable a drive connection between the part its first member is arranged upon and a part its second member is arranged upon. The parts being engaged by the tooth clutch can be a shaft with another shaft or a shaft with a gearwheel or a gearwheel with another gearwheel, or any other combination of two rotating members in the multi-clutch transmission. In the disengaged position of the tooth clutch, the two parts of the transmission provided with respective member of the tooth clutch are disconnected from each other, i.e. not in drive connection, whereby a drive connection is disabled. A gearwheel is normally one member in a gear step, gearwheel pair, gear set or gear stage.
According to the method, during a gear shifting procedure from a currently engaged gear to a predicted gear; the method comprises the steps of:
activating said central synchronizer in to a first active state, such that the speed of the first member of a tooth clutch to be engaged is synchronized with a speed of the second member of said tooth clutch corresponding to said predicted gear,
attempting to engage said tooth clutch, and
if the tooth clutch is determined not to be fully engaged a predetermined period of time after an initiation of an engagement, the following steps are performed:
activating the central synchronizer to the second active state such that the speeds of the first and the second member of the tooth clutch are slightly unsynchronized, and
re-engaging the tooth clutch to be engaged.
Normally the actuating force is kept upon the tooth clutch during the whole procedure, whereby the tooth clutch engages immediately, when the two members of the tooth clutch are unsynchronized.
The method according to the invention enables elimination of a tooth to tooth situation, which prevents an engagement of a tooth clutch, by achieving a speed difference in the synchronized revolutions of the members of the tooth clutch to be connected.
The method can preferably be used during a gear shifting procedure of pre-selected gears, when a new pre-selection of a gear is made. E.g. directly after a performed change of active drive gear or when another pre-selection is desired.
In the application the terms active gear, predicted gear and pre-selected gear will be used. All these terms describe different states of a gear, whereby any gear can be in either of these states, however, only one gear can be in each state at any given time. An active gear is the gear that momentarily is transferring torque from the transmission input to the transmission output. The predicted gear, is the gear which is predicted to be the next active gear and the pre-selected gear is the gear which is pre-selected in the none active part transmission.
In one exemplary embodiment, the method is applied upon a dual clutch transmission, provided with a first and a second input shaft and said first shaft is a main shaft and said second shaft is a countershaft and the tooth clutches are arranged upon the main shaft and the countershaft respectively. The dual clutch transmission is further provided with a central synchroniser, which is displaceable in two opposite directions, corresponding to the first and second active state. In this exemplary embodiment the predicted gear is a third gear, whereby the first tooth clutch is arranged upon the first shaft and is connecting a gearwheel with the first shaft, whereby the first and the second member of the tooth clutch are associated with either of the first shaft and the gearwheel respectively. Normally, during an acceleration phase, when the third gear is predicted a second gear is active and a first gear is or just has been pre-selected. When a third gear is predicted, the pre-selected gear should be changed from the first to the third gear.
In another exemplary embodiment of the method still applied upon a dual clutch transmission, provided with a first and a second input shaft and said first shaft is a main shaft and said second shaft is a countershaft and the tooth clutches are arranged upon the main shaft and the countershaft respectively. The dual clutch transmission is further provided with a central synchroniser, which is displaceable in two opposite directions, corresponding to the first and second active state. In this exemplary embodiment of the method the predicted gear is a sixth gear, whereby the first tooth clutch arranged to connect two gearwheels rotatably arranged adjacent to each other upon the second shaft. The active gear is normally thereby a fifth gear and the predicted gear changes from the fourth gear to the sixth gear, while the vehicle is driving on the fifth gear.
The method can also be applied during a gear shifting procedure changing active gear, e.g., when the vehicle is driving on a first gear and changes to drive upon a second gear.
In another exemplary embodiment of the method still applied upon a dual clutch transmission, provided with a first and a second input shaft and said first shaft is a main shaft and said second shaft is a countershaft and the tooth clutches are arranged upon the main shaft and the countershaft respectively. The dual clutch transmission is further provided with a central synchroniser, which is displaceable in two opposite directions, corresponding to the first and second active state. In this exemplary embodiment of an example of use of the method during a gear shifting procedure changing directly from one active gear to another active gear (which has not been preselected) is given. A momentarily active gear is a second gear, and a preselected gear is a third gear, wherein during a gear shifting procedure from the momentary active gear to a fifth gear, the following is performed;
controlling a first tooth clutch upon a first shaft to a neutral position, in order to disengage said second gear,
activating said central synchronizer in a first direction, such that the speed of a first member of the tooth clutch to be engaged is synchronized with a speed of a second member of the tooth clutch to be engaged, whereby the first and the second members are arranged upon an adjacent gearwheel corresponding to said predicted gear,
attempting to engage said tooth clutch to be engaged with said gearwheel (in order to make said fifth gear active), and
if the tooth clutch is determined not to be fully engaged a predetermined period of time after an initiation of an engagement, the following steps are performed:
activating the central synchronizer in the second direction such that the speeds of the two members of the tooth clutch to be engaged are slightly unsynchronized, and
re-engaging the tooth clutch to be engaged.
Normally the pressure is kept upon the tooth clutch during the whole procedure, whereby the tooth clutch engages immediately, when the tooth clutch and the gearwheel are unsynchronized.
In an exemplary embodiment the first shaft is a main shaft and the second shaft is a countershaft.
In other exemplary embodiments of the method, the method is applied upon a transmission provided with tooth clutches provided upon one or both of the input shafts. The tooth clutches provided upon the input shaft can be synchronised and desynchronized according to the method disclosed.
In other exemplary embodiment of the method, the method is applied upon a transmission provided with a central synchroniser, provided as a first and a second part central synchroniser, where the first part central synchroniser represents the first active state of the central synchronizer and the second part central synchroniser represents the second active state of the central synchroniser.
As disclosed the method can be applied upon dual-clutch transmissions with different configurations, independently on the specific layout of the central synchronizer or upon which shaft the tooth clutches are arranged.
The method is preferably performed by a computer program comprising program code means, wherein said program is run on a computer.
The computer program is preferably carried on a computer readable medium, wherein the program is run on a computer.
A control unit is preferably provided for controlling a utility vehicle, the control unit being configured to perform the steps of the method.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.